Question / Answer

What are the effects of deep survey depths, high mud weights, and tapered strings?

As the measured depth of the wellbore increases, there is a corresponding lengthening of time to receive all of the pulses from downhole.  Make sure to wait several minutes past what you believe to be the final pulse to confirm that you have received all of the pulses.  Also, make sure that you wait the full three to five minutes when taking a survey; it will take longer for the fluid column to settle and the tool to recognize the no-flow situation.  You may find that you need to close the kelly-cock valve or open the stand-pipe bleed off line to completely relieve pressure from the downhole assembly.

Tapered drill strings act to attenuate the signal from the downhole tool.  Make sure that the surface recorder is set to it’s most sensitive readings before attempting to survey.  The signals that you receive may not have the normal shape of previous signals.

Higher mud weights will act to attenuate the signal from the downhole tool.  Be aware of this in your recognition of signals.  Also, higher mud weights will necessitate a longer period for the mud system to reach equilibrium and the tool to obtain a survey.  Again, make sure that you wait the full three to five minutes after the mud flow has stopped for the tool to obtain a survey.